The Cynic School, founded at Athens about 400 B.C., continued in existence until about 200 B.C. It sprang from the ethical doctrine of Socrates regarding the necessity of moderation and self-denial. With this ethical element it combined the dialectical and rhetorical methods of the Eleatics and the Sophists. Both these influences, however, it perverted from their primitive uses; the Socratic ethics was interpreted by the Cynics into a coarse and even vulgar depreciation of knowledge, refinement, and the common decencies, while the methods of the Eleatics and the Sophists became in the hands of the Cynics an instrument of contention (Eristic Method) rather than a means of attaining truth. The Cynic contempt for the refinements and conventions of polite society is generally given as the reason for the name dogs (kúnes) by which the first representatives of the school were known. According to some authorities, however, the name Cynic arose from the fact that the first representatives of the school were accustomed to meet in the gymnasium of Cynosarges.

The founder of the school was Antisthenes, an Athenian who was born about 436 B.C., and was a pupil of Socrates. The best known among his followers are Diogenes of Sinope, Crates, Menedemus, and Menippus. Antisthenes himself seems to have been a serious thinker and a writer of ability. In his theory of knowledge he advocated individualistic sensism as opposed to Plato's intellectualistic theory of ideas; that is to say, he taught that the sense-perceived individual alone exists and that there are no universal objects of knowledge. In ethics he maintained that virtue is the only good and that pleasure is always and under all conditions an evil. Self-control, he said, is the essence of virtue, and a wise man will learn above all things to despise material needs and the artificial comforts in which worldly men find happiness.

Diogenes, generally referred to as "Diogenes the Cynic", is one of the most striking figures in Greek history; at least, his personality with its eccentricities, its coarse humour, its originality, and its defiance of the commonplace, has appealed with extraordinary force to the popular imagination. His interview with Alexander, of which the simplest version is to be found in Plutarch, was greatly exaggerated by subsequent tradition. The followers of Diogenes, namely, Crates, Menedemus, and Menippus, imitated all his eccentricities and so exaggerated the anti-social elements in the Cynic system that the school finally fell into disrepute. Nevertheless, there were in the Cynic philosophy elements, especially the ethical element, which later became a source of genuine inspiration in the Stoic School. This element, combined with the broader Stoic idea of the usefulness of intellectual culture and the more enlightened Stoic concept of the scope of logical discussion, reappeared in the philosophy of Zeno and Cleanthes, and was the central ethical doctrine of the last great system of philosophy in Greece.